Targa is a track add-on, a mod basically... The mod team behind it will probably wait until rFactor 2 is done so they can have everything to work with, and eventually the track will be release to download...

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I have seen nothing which gives any clues this track will be converted anywhere soon. To be honest, I think the modders will concetrate on little tracks first, to get familiar with the way of work, and release content quickly. Getting good content out now, can really set your name on the charts as a modding team. The attention for new mods is huge at this moment.